Ignition Gremlin

[Av8r3400]

As I alluded in the "Milestone" thread, I have been chasing an ignition problem in the Mangy Fox ever since the first start. Because of this, the flight testing has been put on hold.

Here is a description of the problem:

On doing the run-up to 4000 rpm, testing one ignition (A) will drop about 50 rpm. Perfect.

Testing the other ignition (B) gives ~500 rpm drop and the EGTs (located on cylinders 3 & 4) quickly climb through 1500º! Not so perfect.

I have done all the usual stuff.

• Cleaned all grounds
• Checked firing order
• Cut the tips off the plug wires and inspected boots
• New Plugs Gapped to .027"
• Removed modules and checked wiring
• Removed, cleaned, rebuilt, synchronized carburetors
• Then I did it all again...

I spent time today speaking with tech support with CPS, LEAF and Lockwood. The guys at Lockwood cam up with the theory (and they have seen this before) that one of the modules is malfunctioning and could be firing one side 180º off. This would cause the problem I'm seeing.

Each module fires a coil every 180º of crank rotation and each coil fires a pair of plugs (1 & 2 top, 3 & 4 bottom, etc.). If the module is malfunctioning and firing both coils at the same point, then one pair of plugs will ignite the fuel on the way out the exhaust valve, causing the EGTs to skyrocket.

[Av8r3400]

I sent the modules off to Lockwood today to have them tested. (Lockwood is the only place in the US with the testing machine for them)

I have mixed feelings on this. If the module is bad, it will cost me $1200 for new one. If the modules are good then I've got absolutely no clue what's wrong. (But I'll still have money in my account) That's either a win-win or a lose-lose, I'm not sure...



I've heard that kidneys are selling for about $1500 these days.

[HighWing]

"Checked firing Order". Not sure what this means. Would this check have detected the 120 degree off Lockwood is suspecting? The first thing that came to my mind is the possibility that the 1 - 3 or the 2 - 4 lower plug wires might have been switched. Do you have the yellow tags on the ignition wires?

[WWhunter]

Not sure if this makes much differnce, but I thought the plug gap was supposed to be set around 0.021". I need to go check my Zipper plugs I guess.

I just seem to recall there was a 'tighter' gap with one of the piston sets. I do recall the 95 HP Extra-Performance pistons suggested a smaller gap than factory.

[Av8r3400]

When I say check the firing order, I mean the routing of the plug wires to the proper coil. That also means checking that the coils were wired properly to the correct ignition module wires and the plugs were hooked to the proper coils. Thus eliminating the possibility of 1/3 and 2/4 wire mix ups.

Rotax calls for .028" gap on plugs.

[WWhunter]

Yes sir, it was the plugs on the 912 XtraPerformance pistons I originally had in the motor that needed a smaller gap.
www.craftworks.biz/pistonsite/6318.htm